Refractive error is the primary cause of visual development disorders such as amblyopia and strabismus in pre-school age children and the most important cause of visual impairment in school-age children. Current public health policy on vision disorders in children is limited by the lack of evidence on age-specific risk factors and prognostic indicators in children. To address the pressing need for robust empirical evidence and to maximize the value of existing data resources, we formed the Pediatric Eye Disease Consortium(the PED Consortium), that included all existing population-based studies of eye diseases among preschool children, i.e. the Multi-Ethnic Pediatric Eye Disease Study (MEPEDS), the Baltimore Pediatric Eye Disease Study (BPEDS), the Strabismus, Amblyopia, and Refractive Error in Young Singaporean Children (STARS), and the Sydney Pediatric Eye Disease Study (SPEDS). The consortium creates by far the largest repository of population-based survey data on vision health among preschool children (a total of17,056 children aged 6-72 months, including 3,199 Hispanics, 4,316 African-Americans, 5,392 Asians, 3,895 non-Hispanic whites, and 254 individuals of other races, 7,605 aged 6-36 months old, and 9,451 aged 37-72 months old). Making full use of this remarkable resource, we propose to identify demographic, behavioral, and clinical risk factors specific for moderate-severe refractive error, which is associated with much worse prognosis and requires early intervention, and compare differences in risk associations with refractive errors between children aged 6-36 months old and children aged 37-72 months old. With the greater range of exposure variability and improved statistical power provided by the collaboration, we will be able to identify predictors fo moderate- severe refractive error, which is less frequent but more clinically relevant, and explore interaction between aging and other risk factors, which may have been underpowered and therefore not testable in individual studies. Knowledge gained from this study is expected to improve risk stratification significantly by identifying risk factors specific for high refractive rror and for preschool children at different stages of visual development, and provide crucial statistical data for developing evidence-based guidelines for population screening and clinical management of most common pediatric vision disorders at early stages.